Add experts for parallel `rustc`

[Sl1mb0]

There are currently no experts listed for parallel rustc.

I am interested in improving the performance of the compiler via parallel rustc; and as a part of that am planning to join GloRuWriClu to add documentation for it to the rustc-dev-guide.

Can whoever is an expert on parallelism in the compiler list themselves in the experts map? and if they have time/are interested possibly meeting regularly to explain parts of the parallel compiler to as a part of GloRuWriClu?

[Aaron1011]

What's GloRuWriClu?

[Sl1mb0]

What's GloRuWriClu?

Global Rust Writer's Club. I just recently learned about it so I thought it was more well-known.